The use of ultrasound imaging systems requires advanced training and is most often performed by sonographers or physicians who have an intimate knowledge of the anatomy under study, as well as the expected appearance of anatomical features in an ultrasound image. For example, in order to pinpoint the correct probe positioning to acquire an image of a desired anatomical structure (e.g., an organ, lesion or tumor), an operator must coordinate moving the ultrasound probe to the correct location on the anatomy while simultaneously interpreting the resulting images on a display.
Ultrasound has recently been introduced into the field of image-guided radiotherapy (IGRT) in which anatomical structures of interest are imaged immediately prior to a radiotherapy treatment session in order to correctly align the structures of interest to therapeutic radiation beams. Heretofore, ultrasound has most commonly been used for prostate IGRT in which a three-dimensional ultrasound scan (or, in some cases, multiple two-dimensional scans having known three-dimensional positions in space) of the prostate are acquired. These images are used to align the prostate to reproduce a previously-defined treatment plan accounting for daily prostate motion, growth, etc. One challenge is that radiation therapists, who typically have no ultrasound training, are expected to acquire the ultrasound images during the radiation delivery phase of treatment. Because the prostate is always in approximately the same location relative to the bladder, finding it using ultrasound can be relatively easy given some training for the therapists.
However, there are other potential applications for ultrasound-based IGRT in which an operator cannot rely on a consistent location of the anatomical feature of interest, for example, guiding localized breast-cancer radiotherapy treatments in which the main structure of interest is typically a lumpectomy cavity (i.e. the original site of the surgically-removed tumor). While some cavities may be easily found using ultrasound, others can be more difficult to identify. Further, unlike the prostate, which is always in the same general area within the patient, the therapist does not know where to look for the cavity—it can be anywhere within the breast, and therefore requires significant time and experience to find.
As part of radiation therapy, a computed tomography (CT) scan of the area of interest is typically taken for planning purposes prior to the first treatment session. As described in U.S. patent application Ser. No. 10/343,336, entitled “Method and Apparatus for Lesion Localization, Definition and Verification” a three-dimensional ultrasound image may also be acquired immediately before or after acquiring the CT scan. This image is typically acquired by either a CT technologist, radiation therapist or radiation oncologist, who also may not have ultrasound experience, giving rise to the same issues as ultrasound-based IGRT.
Because time and trained operators are scarce in a radiotherapy department, finding an anatomical structure such as a lesion cavity using an ultrasound imaging system can be a limiting task in ultrasound-based IGRT of the breast. Other anatomical sites may share the same problem, such as tumors or nodes in the head and neck region. Therefore, approaches are needed to assist the radiation therapist in finding anatomical structures of interest using ultrasound.